Non-mechanical pencils are traditionally formed by enclosing a marking core (the "lead", often graphite) in a wooden casing using a multi-step manufacturing process that is somewhat costly. The starting material for making wooden casings has traditionally been natural wood such as incense cedar that is machined to form a flat rectangular pencil "slat". Applicant's assignee has been supplying such slats to pencil manufacturers since about 1880. However, environmental concerns have greatly decreased the availability of incense cedar and other natural woods that traditionally were inexpensively and readily available to pencil manufacturers. Further there has been a demand that wood wastes be recycled and that waste wood from manufacturing operations be minimized. As to the latter, an economic consideration exists with both the slat manufacturers and the pencil manufacturers in avoiding the cost of handling and disposal of undesirable wood waste.
In addition, the starting material for pencil casings must meet standards including flexural or breaking strength, rigidity, sharpenability, low density and bondability to the marking core, etc. Substitute material for the wooden casings and for the involved manufacturing process have long been sought. However, it is difficult to form a casing material that is structurally satisfactory, machineable, paintable and will be acceptable to the user as a substitute for the traditional all-wood casing.
Some attempts have been made to manufacture pencil casings from other than natural wood. It has been proposed as hereafter mentioned to manufacture pencil casings by extrusion and subsequent drying of an aqueous pulp of wood or paper with a suitable binder, or to tightly wrap the marking core with paper and the like. In the case of wet-laid composites, such attempts have been problematic because of the necessity of expelling large mounts of water from the slurry.
Further, the wet-laid composite results in loose cores due to poor adhesion with the casings and gives rise to rough casing surfaces when the slat is machined by pencil-making machines and particularly to poor paintability.
Traditionally, each pencil is formed from first and second slats, which have been machined by the slat manufacturer from large 3".times.3".times.96" milled cedar or other timbers in lengths of 48" to 192", oft called "pencil stock". The wood timbers may not be uniform or may contain knots. The result is that only about 50% of the pencil stock is useful to produce pencil slats. The pencil stock is sawn into standard slats each having a thickness slightly more than half the thickness of a pencil and, in the case of making a standard 184 mm pencil, slats having nominal dimensions of 4.8 mm thick by 184 mm length by 71.5 mm wide. Each wood slat is then impregnated with wax and a stain under high temperature and pressure to give the pencil to be manufactured a distinctive color and optimum sharpenability. The wood slats are then dried in a kiln, dimensionally inspected and shipped to the pencil manufacturer.
The pencil manufacturer machines a guide line slot into the slat, for use in guiding the slat through a pencil fabricating machine. Each slat is then grooved, glue is applied, a core is laid in the grooves, and top and bottom slats are then pressed together under pressure until the glue sets. This results in a "pencil slat sandwich." The outwardly facing surfaces of the sandwich are then shaped with a shaping machine which, in the last instant of shaping, also cuts the slat into individual pencils of desired shape. Several coats of paint, varnish or lacquer are frequently applied to the individual pencils. Further, foil wrapping or decoration, and a ferrule and eraser may be added to yield a finished pencil.
U.S. Pat. No. 5,516,472 (Strandex) discloses an apparatus and process for combining an organic fibrous material with a thermoplastic material. The material is processed through a low-temperature extruder into a multiple die system, resulting in an extruded composite material forming a wood-imitating composite for decorative moldings, picture frames, furniture, decks, windows, doors and roofs.
U.S. Pat. No. 5,346,930 (Lydall) discloses wood-substitute fiberboard made by a wet-laid process. The fiberboard is formed in large sheets that are then cut into appropriately sized pencil slats. Unfortunately, it is reported that modified traditional pencil machinery must be used because of the increased density of the fiberboard, requiring special diamond-tipped or carbide cutters for shaping the pencils.
U.S. Pat. No. 3,875,088 (Hasbro) discloses pencil casing compositions, a method, and an apparatus for extruding a casing around a hot marking core to make an extrudate which is subsequently cut into the desired pencil lengths. However the co-extruded marking core and casing in Hasbro which produces a graphite marking core with a plastic component is substantially more flexible than a traditional pencil and does not write or sharpen as well as a traditional pencil. Equipment costs are also high.
Wood substitutes such as disclosed by Strandex, Lydall and Hasbro may suffer from high density, lack of uniformity, inappropriate rigidity, poor sharpenability, poor lacquer adhesion, poor core-casing bonding and excessive surface roughness on the finished pencil resultant from machining. Pencils produced from a wet-laid wood substitute are especially prone to these shortcomings.
Difficulties with the traditional pencil making process which is based on machining of natural wood, include environmental concerns such as diminishing supply of the appropriate wood, reducing waste of wood and resulting high costs which are associated with the process. Thus, there is a need for a substitute for natural wood in the manufacture of pencils. Such substitute should be machineable using existing pencil making equipment and should produce a finished pencil whose density, rigidity, strength, cost, sharpenability, and lacquer adhesion rival pencils made with natural wood slats. The present invention provides such a substitute, hereafter called a "pencil blank", and methods and equipment for fabricating pencil blanks.